Visible light is a part of electromagnetic spectrum that can be sensed by human eyes. There is no accurate scope for visible spectrum. In general, the wavelength of electromagnetic wave that can be sensed by human eyes is 400 nm-700 nm. Normal human eyes are most sensitive to electromagnetic wave with the wavelength of about 555 nm, which lies in green band.
Visible light communication technology is a wireless optical communication technology that is developed following the development of light emitting diode (LED) lighting technology. In comparison with traditional wire transmission, visible light communication provides many advantages such as high transmission power, no electromagnetic interference and energy conservation. Therefore it gains widespread attention and research in the world. The emission system of visible light communication needs to meet double requirements of indoor illumination and communication, and the strength of communication signal is in direct proportion to the illumination intensity. Therefore, good communication and comfortable indoor illumination both request well-distributed indoor illumination.
The modulation bandwidth of LED core is a determinant factor for the channel capacity and transmission rate of visible light communication system. Because of the influence of many aspects such as modulation depth and volt-ampere characteristics, existing visible light communication device is still imperfect. For example, a single LED core provides low power, light output of the core itself is inhomogeneous, and parasitic capacitance produced by high frequency circuit accelerates signal attenuation, which leads to low response frequency and makes the modulation bandwidth unable to meet the requirements of visible light communication.